Add *_remote_toolchain_inputs files for OpenJDK 21 so that RBE
can populate the toolchain dependencies.
Bug: 302395149
Test: ./update.sh 11150980
Change-Id: I6e5010e30d975312949f2d420daba057a55739bb
The OpenJDK21 build requires a 20 or 21 bootstrap JDK, which we don't
yet have prebuilts for. Check in this locally built OpenJDK21.
This will be replaced with a JDK built on the build servers once
they have completed a build bootstrapped from this JDK.
Bug: 302395149
Test: toolchain/jdk/build/build-openjdk21-linux.sh
Change-Id: Ib968726bc96e04c3ca9cb3b964a7be5d028244c1